The present invention relates to a method of polymer purification through continuous soxhlet extraction useful in the manufacture of biocompatible polymeric medical devices. More particularly, the present invention relates to a method of removing contaminants and/or leachables from polymeric materials useful in the manufacture of biocompatible medical devices such as intraocular lenses, corneal inlays and contact lenses using continuous soxhlet extraction.
Medical devices are designed for particular medical applications. Many medical devices are manufactured from polymeric materials, which must be free from contaminants and/or leachables to be useful for the particular medical application for which it is designed. If not removed, contaminants and/or leachables in the material of medical devices may cause adverse effects on patient health or the ultimate outcome of the medical procedure. Such adverse effects can be so severe as to defeat the original purpose of conducting the medical procedure.
In the case of medical devices for ocular use such as but not limited to contact lenses, corneal inlays and intraocular lenses, the devices must be relatively free from contaminants and/or leachables. In medical device applications, contaminants and/or leachables usually form in the polymeric materials of the medical devices as a side product from incomplete curing of the material monomers and/or prepolymers. Material contaminants and/or leachables may likewise be preexisting impurities present in the material monomers and/or prepolymers prior to curing. Because such material contaminants and/or leachables are not uncommon, thorough material extraction is a required step in the manufacture of medical devices and particularly medical devices for ocular use.
There are many ways to extract polymeric medical device materials to remove contaminants and/or leachables present therein. The most commonly used method is batch extraction. Batch extraction is accomplished by placing polymeric medical devices in a container filled with a quantitative amount of xe2x80x9ccleanxe2x80x9d solvent. The clean solvent selected must be capable of swelling the material of the medical device substantially such that contaminants and/or leachables in the material are free to leave the medical device material and enter the solvent phase. The swelled and purified polymeric medical device is then removed from the xe2x80x9cdirtyxe2x80x9d solvent.
Batch extraction of polymeric medical device materials as just described works well in most cases. However, batch extraction may not be sufficiently effective in cases where the target application of the medical device has very stringent requirements in terms of low levels of impurities and/or leachables. Additionally, batch extraction is cumbersome in that it requires the use of large quantities of clean solvent and requires frequent solvent replacement. Frequent solvent replacement causes extraction disruption and increased costs. Batch extraction is likewise not evironmentally friendly in that the process creates large quantities of dirty waste solvent.
Another type of batch extraction is a soxhlet extraction. In a soxhlet extraction, clean solvent contained in a flask is heated to a boil. The solvent vapor evaporates through a vapor arm of a condenser and then condenses within a chamber of the condenser by the running of cold water through a portion of the condenser. The condensed solvent, while still hot, drops down into a reservoir containing the devices to be extracted or purified. The polymeric device materials thus swell and the contaminants and/or leachables are free to leave the device via the solvent. Once the liquid level in the reservoir is above the top level at the peak of the liquid arm, nearly all solvent in the resevoir flows out through the liquid arm and is recycled back to the flask along with the material contaminants and/or leachables. The reservoir is then gradually refilled with condensed hot solvent and the extraction process repeats again, i.e., the devices are again submerged in the rising solvent level until the solvent gets recycled. The soxhlet extraction process as just described is a batch extraction, although slightly better than conventional batch extractions since the solvent is recycled.
Because of the noted shortcomings of batch extraction of polymeric medical device materials, there is a need for an improved method of extracting contaminants and/or leachables from polymeric materials.
Polymeric medical device materials such as those useful in the manufacture of contact lenses, corneal inlays and intraocular lenses are produced with sufficiently low levels of contaminants and/or leachables in accordance with the present invention through a novel continuous soxhlet extraction process. The continuous soxhlet extraction process of the present invention eliminates difficulties formerly encountered in the purification of polymeric medical device materials using batch extraction. The subject continuous soxhlet extraction process is effective in achieving sufficiently low levels of contaminants and/or leachables in cases where the target application of the medical device has very stringent requirements in terms of low levels of impurities and/or leachables. Additionally, the continuous soxhlet extraction process of the present invention is relatively simplistic in that it does not require the use of large quantities of solvent and does not require frequent solvent replacement. Because there is no need for frequent solvent replacement, extraction disruptions and solvent costs are reduced. Additionally, continuous soxhlet extraction in accordance with the present invention is an environmentally friendly purification process since large quantities of dirty waste solvent are not produced.
Accordingly, it is an object of the present invention to provide an effective purification process for polymeric medical device materials.
Another object of the present invention is to provide an effective purification process for polymeric medical device materials with target applications having very stringent requirements in terms of low levels of impurities and/or leachables.
Another object of the present invention is to provide an effective purification process for polymeric medical device materials that reduces clean solvent requirements.
Another object of the present invention is to provide an effective purification process for polymeric medical device materials that reduces solvent waste production.
Still another object of the present invention is to provide an effective purification process for polymeric medical device materials that is economical and environmentally friendly.
These and other objectives and advantages of the present invention, some of which are specifically described and others that are not, will become apparent from the detailed description, drawings and claims that follow.